Case%20Study%202%20Neighborhood%20Models%20of%20the%20Allelopathic%20Effects%20of%20an%20Invasive%20Tree%20Species - PowerPoint PPT Presentation

Title: Case%20Study%202%20Neighborhood%20Models%20of%20the%20Allelopathic%20Effects%20of%20an%20Invasive%20Tree%20Species


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Case Study 2Neighborhood Models of the
Allelopathic Effects of an Invasive Tree Species
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The cast of characters
Tree of heaven (Ailanthus altissima) Introduced
from China in 1784
Lorena Gómez-Aparicio (Instituto de Recursos
Naturales y Agrobiología, Sevilla, Spain)
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Neighborhood Effects of Canopy Trees on Ecosystem
Properties
Estimated footprint of a 30 cm DBH Tree of Heaven
Bottom line Ailanthus increases soil fertility
relative to background effects of the native tree
species
Gómez-Aparicio, L. and C. D. Canham. 2008.
Neighborhood models of the effects of invasive
tree species on ecosystem processes. Ecol.
Monogr. 7869-86
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Allelopathic effects of Ailanthus

• Direct effects of the invasive species on
  nutrient availability are not the whole story.
• Lab studies have isolated an allelopathic exudate
  from Ailanthus (ailanthone)
• Could allelopathy by Ailanthus negate any
  positive effects of the species on soil N and Ca?
• Will the magnitude of the allelopathic effect
  vary for different species of tree seedlings?

Gómez-Aparicio, L. and C. D. Canham. 2008.
Neighborhood analyses of the allelopathic effects
of the invasive tree Ailanthus altissima in North
American forests. Journal of Ecology 96447-458.
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Basic field methods

• Select 20 locations in each of 3 sites with a
  range of abundance of A. altissima within the
  immediate neighborhood (and map the exact
  locations of those trees relative to the sample
  locations)
• Two quadrats at each location, one with activated
  carbon mixed into the soil
• Plant a seedling of each of three native tree
  species into each quadrat

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Statistical model
Response sitej sizel Ailanthus effect (A)
where t treatment (activated carbon or
control), and g can be positive (facilitation)
or negative (inhibition).
where DBH and distance are the size and distance
to neighboring Ailanthus NOTE separate models
were fit using either a 0 or a 2
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Alternate Models

• Our null model Set Ailanthus effect to 1, and
  just fit a model for site and plant size
  effects
• An alternate model test whether the magnitude
  of allelopathic effects was site specific

Response sitej sizel
Response sitej sizel Ailanthus effect (A)
But now, g varies as a function of both treatment
and site
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The error term and PDF

• Error terms varied depending on the response
  variable
• Survival logistic regression (more later)
• Seed emergence binomial
• Growth normally distributed, but with variance
  a power function of the mean

Note estimates of d for the 3 seedling species
were 1.5
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Model Comparison (as Hypothesis Tests)
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Parameter Estimates
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Shapes of the effective allelopathic footprint of
Ailanthus for the 3 native seedling species
The implications of alpha (a) models with a 0
had the highest likelihood (and lowest AIC).
Thus, the density of Ailanthus (stems gt 2 cm
DBH) was more important than their cumulative
biomass
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Responses of native tree seedlings to Ailanthus
allelopathy
Red oak (Quercus rubra) Allelopathy shifts the
neighborhood effect from negative to downright
nasty
without allelopathy
Proportionate Change
allelopathy
Solid circles activated carbon (no
allelopathy) Open circles control
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Sugar maple (Acer saccharum) Allelopathy shifts
the neighborhood effect from neutral to negative
without allelopathy
Proportionate Change
allelopathy
Ailanthus Neighborhood Index (ANI)
Solid circles activated carbon (no
allelopathy) Open circles control
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Red maple (Acer rubrum) Allelopathy shifts the
neighborhood effect from strongly positive to
neutral
Without allelopathy
Proportionate Change
allelopathy
Ailanthus Neighborhood Index (ANI)